Find out about the sport deals that eclipse the proposed $10 million offer for Hawthorn star Buddy Franklin.

It clears the way for Franklin to become a Swan, after the Hawks confirmed they would not be matching Sydney's offer for the restricted free agent.

Hawthorn had three days to match the offer, but said in a statement it would decline, thanking Franklin "for his service and contribution over his nine-year career at the Hawks."

The AFL says it sought a number of written guarantees from the Swans' board before ratifying the nine-year contract, reportedly worth $10 million.

The league started investigating the deal when it was lodged by the Swans last week, to ensure it did not breach the club's salary cap or break any player movement rules.

We understand that nine-year contracts are rare in AFL football, but so too are players the quality of Lance Franklin.

Sydney Swans coach John Longmire

The league demanded the Swans' board provided written guarantees on certain conditions that would be met before approving the deal.

They included a stipulation that the specific financial commitment for each year of the nine-season contract will count towards the Swans' salary cap, even if Franklin retires earlier.

The Swans' board will have to meet with the AFL each year to review how the club are managing their total player payment obligations in regard to the contract.

The AFL also gained assurances from the Swans that they had gained all information needed to properly assess a contract of that length, including medical reviews and long-term financial planning.

AFL general counsel Andrew Dillon said those guarantees had been needed given the unprecedented commitment of total player payment funds to a single player over such a long term.

The league also reiterated to the Swans that the 9.8 per cent cost-of-living allowance built into their salary cap, along with that of Greater Western Sydney, was under review and could be removed or varied from 2015 onwards.

Following Hawthorn's decision to decline matching the Swans' offer, Sydney coach John Longmire said he was pleased to welcome Franklin to the club.

"Lance is a champion player and we are really excited that he wants to continue his outstanding career at the Swans," he said in a statement.

"We understand that nine-year contracts are rare in AFL football, but so too are players the quality of Lance Franklin.

"As a club we will always seek to improve our playing list and we are confident Lance will be a great fit."